As illustrated in Japanese Unexamined Patent Application Publication 2002-71473 there is a known fluorescent light temperature sensor provided with a fluorescent material, a light projecting element for projecting light onto the fluorescent material, a light receiving element for receiving light from the fluorescent material, a light splitting device (a half mirror), and a calculating/controlling unit.
In this type of fluorescent light temperature sensor, light from the light projecting element is projected through the light splitting device onto the fluorescent material. The light from the fluorescent material, which is optically stimulated thereby, is reflected to the light receiving element side by the light splitting device. The temperature in the temperature measurement environment in which the fluorescent material exists is calculated by the processing unit based on the variations in luminous flux (luminosity) from the fluorescent material, detected by the light receiving element, or in other words, based on the decay characteristics of the fluorescent light.
Note that the light projecting element will deteriorate over time, due to the use thereof, causing the intensity of the projected light to decline gradually. Because of this, when it is no longer possible to obtain a predetermined projected light intensity, or when there is a failure in the ignition of the light due to deterioration, then the light projecting element is replaced.
However, the conventional fluorescent light temperature sensor has had the following problems because the deterioration of the light projecting element over time has not been taken into consideration.
Firstly, when the light projection intensity of the light projecting element has declined, it is difficult to perform the temperature measurement accurately based on the variation in the luminous flux of the fluorescent light. When the fluorescent light temperature sensor has a defined correlation between the decay characteristics of the fluorescent light luminous flux, then, for the decay characteristics, the fluorescent light temperature sensor, given the design of the sensor (having to do with the sampling period of the output signal that is outputted from the light receiving element, the processing period in the calculating/controlling unit, and the like), looks for the intensity of the fluorescent light to reach a predetermined level. However, when the intensity of the projected light by the light projecting element has declined, it becomes impossible for the fluorescent material to transition to a state that is stimulated to a predetermined level by the beam from the light projecting element, causing a decline in the intensity of the fluorescent light. Because of this, there is also a decline in the accuracy of the temperature measurement.
Secondly, when it is not possible to obtain the predetermined intensity of the projected light from the light projecting element, or when there is a non-ignition failure due to deterioration, it becomes completely impossible to perform a measurement using the temperature sensor. Because of this, the system or device in which the sensor is incorporated becomes unable to perform operations based on the temperature, causing unanticipated situations for the user. In order to avoid these situations, one may consider replacing the light projecting element on a periodic scheduled basis; however, this is not practical because the deterioration over time will vary depending on the conditions of use.
In contemplation of the situation set forth above, the object of the present invention is to provide a fluorescent light temperature sensor capable of maintaining functionality, as a temperature sensor, in accordance with the deterioration of the light projecting element over time.